Update minimum Python version in documentation

Follow-up to 7e4ff69

Author: speleo3

README.md

@@ -24,7 +24,7 @@ The code in this repository is named _PROPKA 3_ and it is based on the original
 
 ## Requirements
 
-PROPKA 3 requires Python 3.8 or higher.  Additional requirements are specified in the `requirements.txt` file and automatically satisfied when installing with [pip](https://pip.pypa.io).
+PROPKA 3 requires Python 3.10 or higher.  Additional requirements are specified in the `requirements.txt` file and automatically satisfied when installing with [pip](https://pip.pypa.io).
 
 ## Installation
 

docs/source/installation.rst

@@ -5,7 +5,7 @@
 ==============
 
 
-PROPKA 3 requires Python 3.8 or higher. Additional requirements are
+PROPKA 3 requires Python 3.10 or higher. Additional requirements are
 specified in the :file:`requirements.txt` file and automatically satisfied
 when installing with pip_.